Magnetic bearings are bearings that using magnetic levitation to support a load. Magnetic bearings may support moving machinery without physical contact. For example, they can levitate a rotating shaft, providing for rotation with very low friction and no mechanical wear. Active magnetic bearings use electromagnetic suspension, and may include an electromagnet assembly, power amplifiers configured to drive the electromagnets, a controller, and sensors (e.g., gap sensors) with associated electronics. The power amplifiers drive electromagnets on opposing sides of the shaft. The sensors provide feedback to control the position of the rotor within the gap. The controller offsets the current to drive the electromagnets as the rotor deviates from its desired position.
U.S. Pat. No. 5,924,847 issued to Scaringe et al. on Jul. 20, 1999 shows a magnetic bearing centrifugal refrigeration compressor and refrigerant having minimum specific enthalpy rise. In particular, the disclosure of Scaringe et al. is directed toward a vapor compression refrigeration system, such as a water chiller, using a centrifugal compressor with magnetic bearings and a refrigerant, specifically HFC-227ea and HFC-227ca. Magnetic bearings eliminate the problem caused by lubricated bearings to support rotating structure during normal compressor operation.
The present disclosure is directed toward overcoming known problems and/or problems discovered by the inventors.